I bet eBay hates a bitcoin transaction… they cannot get a piece of it! I have worked with Amagi Metals in the past for Bitcoin transactions and the prices and service were great.
I have also sold some ‘slabbed’ gold coins on eBay when I needed some liquidity. Ebay prices are always above spot, but they gotta be as the sellers fees are about 10% on that large transaction. It’s about a wash if you get spot+10%. I wouldn’t deal in raw coins on eBay. If it is slabbed, you have some 3rd party guarantee of what you are getting.